1. Field of the Invention
The invention relates to inverter circuits, and particularly to an inverter circuit with protection function.
2. Description of Related Art
Conventionally, discharge lamps, especially cold cathode fluorescent lamps (CCFL), have been used as backlight sources in liquid crystal display (LCD) panels, driven by an inverter circuit supplying alternating current signals. Often, the inverter circuit includes a power stage circuit and a protection circuit to protect normal operation thereof.
FIG. 4 shows a conventional inverter circuit. The inverter circuit, driving a light source L1, includes a power stage circuit 10, a protection circuit 12, a pulse width modulation (PWM) controller 13, a transformer T1, a first capacitor C11, and a second capacitor C12. The power stage circuit 10 converts a received signal to an alternating current (AC) signal. The first capacitor C11 and the second capacitor C12 are arranged in series and connected between a high voltage terminal of a secondary winding of the transformer T1 and ground, the first capacitor C11 and the second capacitor C12, dividing a voltage output from the high voltage terminal of a secondary winding of the transformer T1, resulting in a divided voltage. The protection circuit 12 is connected to a node formed between the first capacitor C11 and the second capacitor C12, comparing the divided voltage to a reference voltage and outputting a protection signal. The PWM controller 13 is connected between the protection circuit 12 and the power stage circuit 10, controlling output thereof according to the protection signal.
In a conventional inverter circuit, either the first capacitor C11 or the second capacitor C12 is a high voltage capacitor, and the other is a low voltage capacitor. However, the high voltage capacitor is very costly, increasing the overall cost of the inverter circuit. The inverter circuit is disposed on a multi-layer circuit, and the high voltage capacitor is formed between copper layers of the multi layer circuit. Because the multi layer circuit is expensive, the overall cost of the inverter circuit is increased correspondingly.
Therefore, a heretofore unaddressed need exists in the industry to overcome the described limitations.